Exhaust systems are widely known and used with combustion engines. Typically, an exhaust system includes exhaust tubes that convey hot exhaust gases from the engine to other exhaust system components, such as mufflers, resonators, etc. Mufflers and resonators include acoustic chambers that cancel out sound waves carried by the exhaust gases. Although effective, these components are often relatively large in size and provide limited nose attenuation.
Passive valves have been used in a muffler to provide further noise attenuation. However, the proposed valves have numerous drawbacks that limit their widespread use in a variety of applications. One disadvantage with passive valves is their limited use in high temperature conditions. Another disadvantage with known passive valve configurations is that these valves do not effectively attenuate low frequency noise. Further, additional challenges are presented when these types of valves are used in exhaust systems with multiple mufflers.
Attempts have been made to improve low frequency noise attenuation without using passive valves by either increasing muffler volume or increasing backpressure. Increasing muffler volume is disadvantageous from a cost, material, and packaging space perspective. Increasing backpressure can adversely affect engine power. Thus, solutions are needed to more effectively incorporate passive valves within an overall exhaust system.
Still other attempts have been made to use the passive valve in the exhaust system at a location outside of a muffler. For example, the passive valve has been used within an exhaust pipe with a by-pass configuration. The passive valve includes a flapper valve body or vane that is positioned within the exhaust pipe, with the vane being pivotable between an open position and a closed position. The passive valve is spring biased toward the closed position, and when exhaust gas pressure is sufficient to overcome this spring bias, the vane is pivoted toward the open position. In by-pass configurations, the vane provides 100% coverage, i.e. complete blockage, of the exhaust component when in the closed position. When closed, exhaust gases can flow outside of the exhaust pipe that houses the vane via a by-pass pipe that is connected to the exhaust pipe at locations upstream and downstream of the vane. The vane is generally configured such that, during pivotal movement, edges of the vane do not contact inner surfaces of the exhaust component. While use of such a valve improves low frequency noise attenuation, there is additional flow noise caused by turbulence generated at edges of the vane. Thus, while using the passive valve outside of the muffler has addressed certain problems, it has raised additional noise challenges that need to be addressed.
Therefore, there is a need to provide a passive valve arrangement that can effectively attenuate low frequency noises while also addressing additional noise issues introduced by the use of the passive valve itself. This invention addresses those needs while avoiding the shortcomings and drawbacks of the prior art.